Low-melting-point solders have been conventionally used as a joining material for electrically joining an electronic component to a wiring board. Conventionally, in order to enhance the joining strength between the wiring board and the electronic component, the solder serving to join them together has been formed in a fillet form. The solder formed in a fillet form is called a solder fillet. However, the solder fillet is insufficient for enhancing the joining strength, and when the component mounting board is exposed to external impact, the electrical junction between the wiring board and the electronic component may be broken.
Under these circumstances, in order to further enhance the joining strength, one proposal suggests the use of a solder paste including a low-melting-point solder and a thermosetting resin, as a joining material (see, for example, Patent Literature 1). When this solder paste is used in mounting to form a solder fillet, a cured resin film 104 is formed on a solder fillet 103 as illustrated in FIG. 9 (see, e.g., Patent Literature 2). Specifically, the solder paste is applied onto a joint face between an electronic component 102 and a wiring board 101, and then, the solder paste is heated, thereby to melt the solder and soften the thermosetting resin. As a result, the solder and the thermosetting resin are separated from each other, and the solder whose specific gravity is high moves downward to form the solder fillet 103, while the thermosetting resin whose specific gravity is low moves upward to form the cured resin film 104. In that way, the solder fillet 103 is reinforced by the cured resin film 104, and consequently, the joining strength is enhanced.
When an improper mounting of the electronic component (e.g., poor junction) or a defect of the electronic component itself is detected in the produced component mounting board, the component mounting board is subjected to repair work. Here, the repair work is to remove the mounted electronic component from the wiring board, and then re-mount a new electronic component on the wiring board. The electronic component is removed with the use of a tool such as a suction nozzle, while the joint (solder fillet and thermosetting resin) is heated until the solder fillet becomes molten and the thermosetting resin is softened.